1. Field of the Invention
The present invention relates to a mammographic apparatus for taking an image of a breast by detecting the X-ray radiated from an X-ray tube and transmitted through a breast of a subject by an X-ray detector.
2. Description of the Related Art
In the basic radiography with a mammographic apparatus, the X-ray tube T and the X-ray detector D are placed opposed to each other in taking an image at any angle, as shown in FIGS. 10A, 10B and 10C, for example.
Meanwhile, there is a tomosynthetic radiography (tomo-radiography) as means for obtaining a three-dimensional image by use of a mammographic apparatus.
In the tomosynthetic radiography, it is a practice to take an image while rotating the X-ray tube T relative to the breast in the state fixing the breast and the X-ray detector D, as shown in FIG. 11, as an example.
For this reason, the mammographic apparatus, capable of coping with the two radiographic schemes, is required to perform both operations of rotating the X-ray tube T and the X-ray detector D in a synchronous fashion and of rotating the X-ray tube T while placing the X-ray detector at rest.
In order to realize the operations, the X-ray tube T and the X-ray detector D are necessarily arranged on separate frames so that the frames can be rotated independently.
In this case, if desired to enhance the concentricity of rotation path between the X-ray tube T and the X-ray detector D, typically the frames are held for separate rotation about the common rotary axis. In this case, the frames are rotated by separate motors.
In such an arrangement, there is a need to synchronously control the two motors with accuracy in rotating the X-ray tube T and the X-ray detector D in a synchronous fashion. This, however, is not easy to realize.
Meanwhile, there is proposed a structure to move a frame fixed with an X-ray tube along an arcuate path (see JP-A 2003-305031, for example). However, with this structure, deterioration is encountered in the rotation-path concentricity of between the X-ray tube T and the X-ray detector D.
In this manner, there is conventionally a difficulty in implementing a synchronous rotation while enhancing the rotation-path concentricity of between the X-ray tube T and the X-ray detector D.